The present invention relates generally to the field of organometallic compounds. In particular, the present invention relates to the certain organometallic compounds suitable for use in vapor deposition processes such as, but not limited to, atomic layer deposition (ALD) or cyclic chemical vapor deposition (CCVD), that may be used to form, for example, a gate dielectric or capacitor dielectric film in a semiconductor device.
With each generation of metal oxide semiconductor (MOS) integrated circuit (IC), the device dimensions have been continuously scaled down to provide for high-density and high-performance such as high speed and low power consumption requirements. Unfortunately, field effect semiconductor devices produce an output signal that is proportional to the width of the channel, such that scaling reduces their output. This effect has generally been compensated for by decreasing the thickness of gate dielectric, thus bring the gate in closer proximity to the channel and enhancing the field effect which thereby increasing the drive current. Therefore, it has become increasingly important to provide extremely thin reliable and low-defect gate dielectrics for improving device performance.
For decades, a thermal silicon oxide, SiO2, has been mainly used as a gate dielectric because it is stable with the underlying silicon substrate and its fabrication process is relatively simple. However, because the silicon oxide gate dielectric has a relatively low dielectric constant (k), 3.9, further scaling down of silicon oxide gate dielectric thickness has become more and more difficult, especially due to gate-to-channel leakage current through the thin silicon oxide gate dielectric.
This leads to consideration of alternative dielectric materials that can be formed in a thicker layer than silicon oxide but still produce the same or better device performance. This performance can be expressed as “equivalent oxide thickness (EOT)”. Although the alternative dielectric material layer may be thicker than a comparative silicon oxide layer, it has the equivalent effect of a much thinner layer of silicon oxide layer.
To this end, high-k metal oxide materials have been proposed as the alternative dielectric materials for gate or capacitor dielectrics. Metal-containing precursors may also be used by themselves or combined with other metal-containing precursors, such as, for example, Pb(Zr,Ti)O3 or (Ba,Si)(Zr,Ti)O3, to make high dielectric constant and/or ferroelectric oxide thin films. Because the dielectric constant of metal oxide materials can be made greater than that of the silicon oxide, a thicker metal oxide layer having a similar EOT can be deposited. As a result, the semiconductor industry requires metal-containing precursors, such as, for example, titanium-containing, zirconium-containing, and hafnium-containing precursors and combinations thereof, to be able to deposit metal-containing films such as, but not limited to, oxide, nitride, silicate or combinations thereof on substrates such as metal nitride or silicon.
Unfortunately, the use of high-k metal oxide materials presents several problems when using traditional substrate materials such as silicon. The silicon can react with the high-k metal oxide or be oxidized during deposition of the high-k metal oxide or subsequent thermal processes, thereby forming an interface layer of silicon oxide. This increases the equivalent oxide thickness, thereby degrading device performance. Further, an interface trap density between the high-k metal oxide layer and the silicon substrate is increased. Thus, the channel mobility of the carriers is reduced. This reduces the on/off current ratio of the MOS transistor, thereby degrading its switching characteristics. Also, the high-k metal oxide layer such as, for example, a hafnium oxide (HfO2) layer or a zirconium oxide (ZrO2) layer has a relatively low crystallization temperature and is thermally unstable. Thus, the metal oxide layer can be easily crystallized during a subsequent thermal annealing process used to distribute the n and p type dopants previously injected into source/drain regions of the device. Crystallization can lead to the formation of grain boundaries in the metal oxide layer through which current can pass thereby degrading the performance of the dielectric oxide as an insulator. Crystallization can also lead an increase in the surface roughness of the metal oxide layer which can also lead to current leakage and dielectric deterioration. Further, the crystallization of the high-k metal oxide layer can also undesirably affect subsequent lithographic alignment processes, due to irregular reflection of the light by the rough surfaces.
In addition to minimizing side reactions with the substrate upon which the metal-containing precursor is deposited, it is also desirable that the metal-containing precursor is thermally stable, and preferably in liquid or low melting solid form. Group 4-containing metal films, for example, are typically deposited using a vapor deposition (e.g., chemical vapor deposition and/or atomic layer deposition) process. It is desirable that these precursors are thermally stable during vapor delivery in order to avoid premature decomposition of the precursor before it reaches the vapor deposition chamber during processing. Premature decomposition of the precursor not only results in undesirable accumulation of side products that will clog fluid flow conduits of the deposition apparatus, but also may cause undesirable variations in composition of the deposited gate dielectric, high dielectric constant and/or ferroelectric metal oxide thin film.
Although metal enolate species have been reported as intermediates and catalytic chemical species used in organic synthesis (Tetrahedron Lett. FIELD Full Journal Title: Tetrahedron Letters 22(47): 4691-4), they have not been isolated as low melting, cleanly evaporating and thermally stable molecules for use in thin film deposition processes, as those described below.
Other prior art includes; US2007/0248754A1, U.S. Ser. No. 11/945,678 filed on Nov. 27, 2007, Applicants' co-pending application U.S. Ser. No. 12/266,806 which was filed on Nov. 11, 2008; Applicants' patents U.S. Pat. No. 7,691,984, and U.S. Pat. No. 7,723,493.
Accordingly, there is a need to develop metal-containing precursors, preferably liquid Group 4 precursors, which exhibit at least one of the following properties: high thermal stability, high chemical reactivity and low melting points.